The present invention relates to fluid dispensing systems and method of use thereof, primarily in industrial applications requiring the dispensing of fluids such as epoxies, silicones, adhesives, etc. More particularly the present application relates to those applications where preciseness and accuracy of the amount dispensed is important.
Dispensing consistent, controllable, accurate measured amounts of fluids with varying viscosities at an assembly plant workstation is a long-standing problem facing manufacturers concerned with efficient precision product. As can be imagined, quality production requires that an optimum amount of fluid be consistently dispensed. Too little fluid and the product might be come apart and/or be unsafe to use as designed. Too much and the product might be unsightly, messy, or unsafe. Further, wasted fluid wastes money.
One prior art solution to this problem is to provide an applicator having a reservoir of fluid and attached to a driving force needed to extrude the fluid. These systems use syringes with air pressure driving the piston to expel the fluid.
Also known in the art is the use of syringe pumps that continuously introduce a fluid into an intravenous tube. These devices usually employ a gravity-fed tube attached to a reservoir (usually an intravenous bag or bottle) and a motor-driven pump that regulates the flow of fluid via a cam that alternately compresses and releases the tube. This technology lacks the precision requirements of industry.
More pertinent to the industrial context is the pneumatic pressure-driven fluid dispenser, which has a syringe containing the fluid to be dispensed attached to a controller that also controls a compressed air supply (usually xe2x80x9cshop airxe2x80x9d). Fluid is dispensed when the controller introduces the compressed air into the syringe that depresses the syringe piston a specific distance. A major disadvantage of this technology is that, as fluid is dispensed, an increasing void volume is created behind the syringe plunger. Thus, since the same volume of compressed air is introduced to the syringe behind the plunger regardless of the void volume of the syringe, there is substantial variability in the amount dispensed during successive operations of the syringe as the fluid is depleted in the syringe.
It has been recognized that mechanical control of a syringe plunger would increase the accuracy and consistency of fluid dispensing. U.S. Pat. No. 4,848,606 to Taguchi et al. shows an apparatus for dispensing a predetermined volume of paste-like fluid that has a motor attached to one end of a threaded screw rod and a nozzle holder functionally connected to the screw rod. To control the Z-axis position of the nozzle, the motor is operated, thereby rotating the screw rod and causing the nozzle holder to travel up and down the rod threads. The dispensing is accomplished by a second motor and screw rod combination, this time having a piston-driving device coupled to a piston that is disposed within the nozzle. Operation of the second motor rotates the second screw rod, causing axial movement of the piston and subsequent fluid dispensing from the nozzle.
One drawback of the Taguchi et al. device is that it uses an indirect mechanical coupling between the rotating motor and the piston or plunger of a dispenser. Another drawback is that it cannot be rack-mounted and put into a production assembly line system.
However, a fundamental drawback to the Taguchi et al. and similar devices is that they dispense fluid from a syringe by moving the syringe, not the plunger. Because these devices employ stepper motors, rotation of the rods attached thereto by definition results in axial movement of the means holding the syringe and, thus, the syringe itself, not of the rod and a plunger attached thereto. This is because stepper motors must be attached to the end of the rod that they drive, they do not allow the rod to pass through the axis of the motor such that the rod can move axially relative to the motor. Indeed, Taguchi et al. Make things more complex by requiring two stepper motors and two drive rods, one to control the axial position of the nozzle and one to dispense fluid.
Another major drawback of all these dispensers is that the xe2x80x9cdosagexe2x80x9d of fluid to be extruded cannot be controlled as precisely as desired. Most of the references use translated rotational motion to create relative linear movement of a plunger, whether by driving a plunger along the threaded member or using the threaded member to drive other mechanical plunger-driving means.
In contrast, use of a linear actuator instead of a stepper motor would allow the rod itself to be driven axially through the actuator thereby achieving direct control of a syringe plunger without complex mechanical means.
In addition to enabling precise volumetric control and ease of use, a practical fluid dispenser should be easily incorporated into an assembly line workstation.
Another limitation in prior art devices, especially dispensers of higher viscosity fluids, is that there is a residual dispensing, leakage or oozing of the fluid after the driving mechanism has stopped slowly expelling extra, unwanted fluid. To accommodate the time and this extra fluid, the dispensing apparatus cannot be moved to the next location since the leaking fluid would be drip onto unwanted areas as the dispenser was moved to the new location. A significant amount of time must pass before moving to allow the leaking to stop. This limitation prevents accuracy, precision and time efficient operation of the dispensing apparatus.
Another application of fluid dispensing requires mixing of components in precise and repeatable proportions. For example, even for the home workshop epoxy dispensers provide a dual syringe assembly with a single hand operated surface connected to the pistons located within the syringes. This allows for the simultaneous dispensing of the two components in rough proportions needed to adequately dispense the epoxy. This apparatus demonstrates an application of dispensing mixing fluids but this apparatus lacks the precision and repeatability required by industry. There is a need for accurate, precise proportional dispensing of fluids that commingle as they are dispensed.
A U.S. patent to Gardos et al. No. 5,816,445, discloses a two-part fluid dispenser with adjustable dispensing ratios. Air pressure drives pistons in cartridges whose linear motion is measured and controlled by a microprocessor or manually to dispense proper amounts. This system lacks accuracy and precision since the piston are not physically connected to and controlled from the microprocessor. The invention is directed towards fluids of differing viscosities. An air driven pinch tube controlled by the microprocessor closes the channel to the work piece thereby stopping the flow out of the system. Howevcer, this techniques does not fully prevent leaking. To provide some accuracy, the cartridges are pressurized and therefore need to be shrouded by to prevent distortion of the plastic cartridges during use. This system discloses using predefined and loaded cartridges to provide specific ratios of material delivered. The system drives the pistons in each cartridge the same distance, but the different cartridges will output different amounts as determined by the physical differences in the cartridges. This arrange is fixed, inflexible and limited in that other ratios can only be provided by replacing the cartridges, but the range of ratios is fixed by the availability of cartridges.
A U.S. patent to Weston, No. 5,348,585 discloses a controlled motor driven dispenser from a cartridge. There is a rotating drive rod that is mechanically interconned to move the piston in the cartridge. The arrangement shows that the motor and other parts of the mechanism move. This is a costly complexity and limitation of the invention. Moreover, the mechanism disclosed uses a rotating drive shaft and a threaded rod for effectuating the motion. Apparently form the patent the piston rotates which is another limitation of the design along with the complexity.
Another limitation of the prior art, mentioned above, is that it is desirable to eliminate dripping after a given amount of fluid has been dispensed. Occluding the output channel, as in the Gardos et al. patent discussed above, does not work well over the wide range of fluids and viscosities used in these system.
It is an object of the present invention to provide a solution for the above problems and limitations found in the prior art.
Accordingly, an object of the present invention is to provide a means for repetitively dispensing a precise and optimum amount of fluid.
A further object of the present invention is to provide a fluid dispensing means having sufficient rigidity, durability, and lightweight to meet production line requirements.
Another object of the present invention is to provide such a dispensing means that dispenses and commingles two or more fluids.
Still another object of the present invention is to provide a co-mingled output of two or more fluids in substantially any desired proportions.
Yet another object of the present invention is to provide a fluid dispensing means that drives a non-rotating rod that is interlocked and fixed to the piston within the syringe, thereby allowing the drive controller to reverse the direction of the piston.
Still yet another object of the present invention is to provide a dispensing process which eliminate dripping.
Yet another object of the present invention is to provide a system that uses preloaded syringes and cartridges wherein the contents therein never are exposed to the operating personnel.
Other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments thereof taken in conjunction with the accompanying drawings.
The present invention is a fluid dispensing system, and method of use thereof primarily in industrial applications requiring an accurate, precise dispensing of fluids with varying viscosities, such as water, epoxies, silicones, adhesives, solder paste, single component, two component, filled, premixed, frozen, etc.
The dispenser has a syringe disposed within an adapter unit that is attached to an dispenser apparatus. This apparatus is controlled by a microprocessor-based controller that can be programmed to dispense precise volumes of fluids based on syringe size, including length, inside diameter, dispense volume, dispense rate, backoff (see below), method of dispensing, and control of automated or manual dispense actions, and fluid viscosity.
An important advantage of the present invention is the linear driving of the piston in the syringe without rotating that piston. In the present invention the piston is fixed to the drive shaft and the arrangement linearly drives the piston without rotating by use, in a preferred embodiment, of a linear actuator.
Another feature of the present invention is reversing the motion of the piston to achieve xe2x80x9cbackoff.xe2x80x9d This feature is enhanced by controlling the timing of the xe2x80x9cbackoffxe2x80x9d where the dispensing is stopped for a programmable length of time before reversing direction. As described above, for many fluids being dispensed unwanted leaking will occur. The present mechanism fixes the drive piston to the drive rod wherein the controller may drive the piston forward a precise distance dispensing fluid and then drive the piston backwards a precise distance to prevent any leakage. In a preferred embodiment a trial and error approach has been found to be an efficient way to determine for any given fluid the amount of back off needed to achieve the precision and accuracy for any particular application. In a preferred embodiment any mechanical backlash, when changing directions of the piston, is compensated by the trial and error approach.
The dispenser can be mounted for operation commercially available X-Y-Z axis tables, wherein the volume of fluid dispensed can be programmed by the controller or regulated by an external source to maintain the desired volumes at the desired rates. The controller may be a separate assembly that is rack mounted nearby.
The system comprises an applicator capable of accommodating one, two or more syringes or cartridges and piston assemblies, with the controller attached by a control tether to an electronic control unit. The applicator is provided with a linear actuator that displaces a drive rod a specific distance in response to an electronic drive signal generated by the controller. The electronic drive signal is generated by the controller in response to receipt of an actuator signal generated by either the operator, as by a finger switch attached to a handheld applicator or a footpedal, or a pre-programmed input, such as a microprocessor. Displacement of the drive rod creates a positive pressure on a fluid contained in the syringe, thereby causing fluid extrusion from the syringe. As can be expected, because the drive rod is displaced a precise distance forward, stopped and then displaced in reverse, this system allows for very precise control of the volume of fluid extruded.
The present invention has an advantage that it provides a precise, optimum amount of fluid to be repetitively dispensed quickly resulting in efficient operation.
In a preferred embodiment, there may be multiple self-contained syringes or cartridges arranged with common outputs where the co-mingled proportions are programmable by the controller. These systems may be arranged in an automatic work station and may be powered from a battery or line power with the appropriate converters and interface electronic, as are well known in the field.